1. Field of the Invention
The present invention relates to a novel process for producing benzanthrone, more particularly, it relates to a novel process for producing benzanthrone by reacting a specific hydroanthraquinone with acrolein.
2. Description of the Prior Art
Benzanthrone is an important compound as the starting material for producing Indanthrene dyes and pigments.
It has been known to produce benzanthrone by the following processes. (1) Anthraquinone is dissolved into sulfuric acid and a mixture of metallic powder and glycerin is added to the solution to reduce anthraquinone and simultaneously, the reaction product is further reacted with the compound resulted by dehydration of glycerin in an addition-reaction (B10S 987 and F1AT 1313). (2) Benzanthrone is produced by reacting an anthrahydroquinone ester such as acetate and sulfate which is obtained by reducing and esterifying anthraquinone, with acrolein in the presence of a dehydration catalyst such as sulfuric acid and piperidine in a solvent of acetic acid. (DRP 720,467). (3) Benzanthrone is produced by condensing .alpha.-benzoylnaphthalene at higher than 150.degree. C. in the presence of aluminum chloride catalyst or at 120.degree. C. in the presence of iron chloride catalyst. (DRP 239,761).
However, in the process (2), the expensive metallic powder is used to reduce anthraquinone and anthraquinone is esterified with acetic anhydride etc. whereby the complicated steps are needed, and the reaction velocity in the production of benzanthrone is slow and the cost is expensive and the separation of the metal ions is not easy in the waste treating step.
In the process (3), the yield is too low such as 75% and many reaction steps are needed and large amounts of the by-products are produced. Accordingly, it is not an industrial process.
In the process (1), which is mainly employed as an industrial process, 7 to 10 times of sulfuric acid to anthraquinone should be used as the solvent for anthraquinone. Accordingly, when benzanthrone is precipitated by diluting the reaction product with water, a large amount of dilute sulfuric acid waste having high COD load may be discharged. The precipitated crystals are fine whereby the filtration is inferior. The compounds produced by reducing anthraquinone are unstable in sulfuric acid at the elevated temperature and the control of temperature in the addition-cyclization reaction is not easy and sometimes, the bubbling is caused whereby the control of the addition-cyclization reaction is not easy. Moreover, the metal powder having uniform particle size distribution should be used as the reducing agent whereby it is expensive. There is high possibility of the accident of explosion on hydrogen gas generated by using the reducing agent. The separation of metal ions discharged in the waste water is not easy. These disadvantages have been found.
The inventors have studied to overcome the disadvantages found in the conventional processes.